Increasingly, television broadcast signals include logos that are displayed on television screens over the broadcast programs as station identification. If logos stay on the screen for considerably long periods of time without change in their intensities, colors, patterns and locations, they may be annoying, and can cause problems such as the well-known screen burn on High Definition TV (HDTV) sets. In general, logos are classified into three types: opaque logos, transparent logos and animated logos. Because transparent and animated logos change their brightness and colors along with the background video content, or move around from time to time, they are unlikely to cause screen burn on HDTV sets. By contrast, opaque logos are more problematic, because they usually stay on the screen for considerably long period of time without changing their intensities and locations.
As such, techniques have been developed for detecting the logos within the broadcast video signals, and removing or processing the logos to avoid the above problems. U.S. Pat. No. 5,668,917 relies on the repetitive characteristic of opaque logos in detecting of logos and commercials. The similarity among successive frames is examined and then the matching segment is eliminated. However, as the transmission channels normally introduce some noise to the video signal, the similarity within the repeated logo region among sequential frames can be greatly reduced, specially when the noise reaches a relatively high level. In this case, the similarity check may not be good enough for logo detection.
In another related invention, U.S. Pat. No. 5,920,360, intensity change vectors for detecting fade transitions were defined. Though this method may have higher noise immunity by using a coarse level of spatial information, it does not utilize the temporal information carried in video sequences.